The (pi(-), gamma gamma) reaction in nuclei and the sigma meson in the medium

A theoretical analysis of the (π−,γγ) reaction in nuclei is made in order to find the viability of this reaction to test modifications of the σ meson mass in nuclear matter. The ππ correlation in the scalar-isoscalar channel in nuclear matter could, in principle, manifest itself in this reaction since it plays an important role in the ππ→γγ mechanism. But we conclude that this effect is hardly visible in this reaction due to the strong background of the pion-Bremsstrahlung terms. Only with some special cuts and for some polarization states are the effect visible at the cost of a strong reduction in the cross section